Bulk acoustic wave (BAW) devices or film bulk acoustic resonator (FBAR) devices are widely used as RF filters in 4G LTE (Long Term Evolution) devices in order to obtain a high Q factor.
However, through-silicon vias (TSV) are performed through a cap substrate that has been assembled to the FBAR substrate according to conventional wafer-level packaging methods. In a conventional method, since the metal connection member of the cap substrate and the metal connection pad of the FBAR substrate may be of the same material or different materials and join at a contact interface, the contact interface will have a natural oxide layer resulting in a change of resistance at the contact interface. As shown in FIG. 1, the cap substrate 101 is assembled to the metal connection pad (indicated as an oval circle in FIG. 1). The bonding process of the contact interface between the metal connection pads of the cap substrate and the FBAR substrate may affect the resistance of the through hole via. Therefore, the conventional method of assembling the cap substrate to the BAW or FBAR device may adversely affect the resistance of the through via as an electric connecting element to an external circuit.
Conventional approaches utilize gold to form a connection 102. However, gold is expensive and may increase the manufacturing costs. Because gold is a heavy metal that may cause contamination resulting in a shorter minority carrier lifetime of a CMOS (complementary metal oxide semiconductor) device. Thus, it is difficult to meet the production requirements.
Therefore, there is a need to solve the problems of poor resistance in the contact interface between the metal connection pads of FBAR or BAW devices in the conventional packaging processes.